The present invention relates to a process for producing dried singulated cellulose pulp fibers, and more particularly, to a process for producing dried singulated cellulose pulp fibers including the step of using a jet drier to dry the pulp.
Dried singulated cellulose pulp fibers are desirable for many products from absorbent personal articles to a strengthener in concrete. Currently, in the most common process of making singulated fibers, a roll of conventional pulp fibers is hamermilled into singulated fibers. This process is energy and time intensive, requiring many steps and pieces of processing equipment. Each piece of processing equipment requires a significant capital expenditure and occupies valuable factory floor space. Further, the current hammermilling process often produces fibers with undesirable physical properties, such as low kink, curl, and twist.
This dry singulated pulp will also contain knots of fiber, sometimes referred to as nits or nodules. Knots are fiber clumps that remain strongly adhered to one another as can be seen by placing a small portion of pulp into a clear beaker of water and stirring the water to mix the fibers. Most of the fiber will mix into the water as singular fibers, however there will be fiber clumps that are readily visible. The fiber clumps or knots are undesirable by-products of the hammermilling process. The amount of knots in a pulp that has been hammermilled can be quantified by using a screening system with acoustical energy used as the means to classify the fiber into sizes of knots, accepts and fines. It is desirable to have low knots and fines and high accepts where the accepts are the singulated fibers.
Canadian Patent No. 993618 (Estes, 1976) describes a process for producing a low density fluff pad or batt from individual fibers that have significant kink and interlocking to provide improved batt strength and higher bulk. In accordance with the process, wet pulp is separated into individual fibers during the drying stage. The process uses fluid jet drying equipment that employ air-jets or steam-jets for separating the fibers. The fibers are laid on a perforated screen upon exiting from the jet drier. The fibers produced by the process of the Canadian patent, however, have a very high knot content, which as stated above is an undesirable characteristic.
This invention provides a process for forming singulated and dried fibers that have a relatively low knot content. In accordance with the process, wet pulp and air are introduced into a jet drier. The pulp is dried in the jet drier to form singulated pulp fibers. The pulp is removed from the jet drier and separated from the air. The process may be used on several types of feed pulp and on treated feed pulp. The product formed by the process has advantageous properties such as a low knot count, a low fines count, as well as improved kink, curl and twist. The apparatus for carrying out the process may include a pretreatment station for supplying a treatment substance, a pulp feed device designed only for pulp, a pulp feed device designed for pulp and foam suspensions of pulp, and/or a fiber separation station having a vacuum conveyor.
In accordance with the process described above, the wet pulp is treated with a treatment substance before drying to reduce the knot content of the pulp fibers. The process also includes producing singulated pulp fibers by introducing wet pulp and air into a jet drier through a rotary airlock. The rotary airlock has vanes and a housing, with the end of the vanes being spaced from the housing by a distance sufficient to prevent wet fibers from clogging the airlock. The process includes producing singulated pulp fibers by withdrawing the fibers from said jet drier in an air stream at a velocity sufficient to prevent the fibers from knotting. The process also includes producing singulated pulp fibers by withdrawing the pulp fibers from an outlet from said jet drier under a partial vacuum.
In one embodiment, the pulp supply station includes a treatment supply source for delivering a treatment substance to the pulp. In another embodiment, the pulp supply station includes a pulp feed device coupled to the pulp intake for delivering the feed pulp to the pulp intake while minimizing the amount of air flow through the pulp supply station. The pulp feed device may be a rotary airlock including a rotor housing and a rotor rotatably mounted within the rotor housing, the rotor having rotor vanes for transporting the feed pulp. The rotor vanes and rotor housing are sized so that a gap exists between the rotor vanes and the rotor housing to prevent the feed pulp from jamming the rotary airlock. In a further embodiment, the pulp supply station may further include a foam feeder interposed between the pulp feed device and the pulp intake for mixing a surfactant with pulp and directly injecting foamed pulp mixture into the jet drier.
In a still further embodiment the fiber separation station includes a vacuum conveyor having a screen for passing outlet air and retaining fibers to form a mat of fibers on the screen. The vacuum conveyor may have a first roller, a second roller, a primary fan, a secondary fan, a primary fan vacuum box, and a secondary fan vacuum box. The screen is a continuous loop draped about the first and second rollers so that the screen has an upper portion and a lower portion. The upper portion of the screen has an upper and lower surface. The upper surface of the screen is associated with the outlet flow conduit. The primary fan vacuum box is associated with the lower surface and in flow communication with the primary fan. The primary fan vacuum box is positioned between the lower and upper portions and directly beneath the outlet flow conduit. The secondary fan vacuum box is associated with the lower surface and in flow communication with the secondary fan. The secondary fan vacuum box is positioned between the lower and upper portions and between the primary fan vacuum box and the second roller. The primary fan provides vacuum to the primary fan vacuum box and the outlet flow conduit. The secondary fan provides vacuum to the secondary fan vacuum box and the upper surface.
The present invention thus provides a dried singulated cellulose pulp fiber product as well as an apparatus and a method that enable forming singulated and dried fibers. The process may take wet pulp directly from a pulp mill and produce a singulated product from the never-dried pulp by using a drying process that singulates the pulp directly. This process forms fibers with greater kink, curl, and twist than hammermilled fibers. A further advantage is the ability of the present invention to produce fibers having a low knot and fines content. Another advantage is the treatments that can be performed on the pulp that are difficult or impossible to perform on a roll of dried pulp. Treatments can be done on the never-dried pulp that reduce the amount of knots, increase production rate, and/or form fibers having desirable characteristics.